Cold-cathode valve circuit



Oct. 23, 1956 F. s. GOULDING ET AL 2,768,330 COLD-CATHODE VALVE CIRCUIT Filed Dec. 3, 1952 FIG.|

+ FIG.2

IN VEN TORS FREDERICK SYDNEY GOULDING CHRISTOPHER HALY TOSSWILL' AGENT 2,768,330 Patented Oct. 23, 1956 Ece United States Patent Cd 2,768,330 COLD-CATHODE VALVE: CIRCUIT Application December 3,1952, Serial No. 323,812 Claims priority, application Great Britain D'ecemberS, 19$

5 Claims. (CL 315-168)- The present invention relates to cold cathode circuits. More particularly, the invention relates to circuits for cold-cathode valves or electron discharge tubes having an auxiliary cathode as disclosedin United States Patent No. 2,736,840, issued February 28',- 1956,.v to Tosswill. The circuits of the invention provide for the triggering of such tubes bynegative input'p'ulses.

Negative pulse operation of a cold-cathode trio'de tube is possible by biassing the trigger electrode to a negative potential so as to benear the striking point and superimposing the negative pulse on the trigger electrode bias to fire the tube. In another arrangement negative pulse operation is achieved by feeding the negative pulse to the cathode of a tube having a positive bias on the trigger electrode. Such arrangements have a charge sensitivity of the order of 500 micro-micro-coulombs.

In the circuit of the present invention the negative input pulses for triggering the tube are fed to the auxiliary cathode. A charge sensitivity of the order of micromicro-coulombs is obtained.

The circuit of the invention comprises a cold-cathode tube having an anode, a trigger electrode, a main cathode and an auxiliary cathode between trigger electrode and main cathode. The circuit further comprises means for setting up a corona discharge between the trigger electrode and auxiliary cathode, an input circuit connected with the auxiliary cathode for feeding negative pulses to the tube to withdraw charge and hence increase ionization to set up a glow discharge between the trigger electrode and the main cathode so that the tube is discharged between anode and main cathode, and means for quenching the discharge in the tube.

In a modified form of the circuit of the present invention a rectifier is included in series with th input circuit in a sense to prevent positive pulses being fed back into the input circuit and a connection is provided to feed a small current through the rectifier in the absence of input pulses.

A ratemeter is provided for negative input pulses.

The operation of the circuit of the invention will now be described more fully with reference to the accompanying drawing, wherein:

Fig. 1 is a schematic diagram of an embodiment of the circuit of the present invention; and

Fig. 2 is a modification of the embodiment of Fig. 1.

In Fig. 1, a high tension source is provided between a terminal 1 and ground line 2. An electron discharge tube 3, having an anode 4, a trigger electrode 5, an auxiliary cathode 6 and a main cathode 7 is coupled to the positive side of the high tension source via anode quench resistor 8 in series with a rate circuit 9 comprising resistor 10, meter 11 and condenser 12. The cathode of the tube 3 is connected to the ground line through a limiting resistor 13. A resistor 14 connected to the trigger electrode 5 and a resistor 15 connected to the auxiliary cathode 6 provide a path for a corona discharge current to pass across the trigger electrode/auxiliary cathode gap. The

input circuit comprises an input terminal 17 and a condenser 18- connected to' the auxiliary cathode 6. A condenser 16 connected to the trigger electrodeS is provided to maintain the potential of that electrode when charge is-Withdrawn on receipt of a negative pulse at the auxiliary cathode 61 A main discharge condenser 19 is provided between the anode4'a'nd" ground.

In the quiescent state of the circuit the potentials at the various electrodes of the tube 3 are, for example, anode at 160 volts, trigger electrode at 125 volts (determined by the corona voltage drop from the trigger electrode to'auxiliary cathode), auxiliary cathode at a few volts positive, and the main cathode at ground potential. On the arrival of a negative pulse of comparatively small amplitudeat the terminal 17 sufiicient charge is withdrawn to'increase' the ionization and raise the voltage drop across the trigger electrodefauxiliary cathode space slightly so that the corona discharge between trigger electrode and auxiliary cathode passes, after a brief time delay determined by transit phenomena in the tube, into a glow discharge between trigger electrode andmain cathode. With this glow discharge, the trigger electrode potential drops toxabout' volts and the condenser 16 discharges into the tube. The large amount of charge drawn from condenser 16 produces sufiicient' ionization in the tube 3 to cause the main discharge between anode and cathode of said tube, discharging condenser 19 through said tube. The auxiliary cathode potential rises to about 75 volts and the anode potential drops immediately to a potential of approximately volts.

The resistor 8 limits the current flowing through tube 3, when condenser 19 has discharged, to a value that does not sustain discharge in the tube. The condenser 19 recharges by current drawn through the rate circuit 9 and resistor 8, and the other volt-ages re-establish themselves to those existing in the quiescent state.

Modifications may be made to the circuit described above and these are illustrated in Fig. 2, wherein corresponding parts are correspondingly designated. In the modification of Fig. 2 the condenser 16 may be replaced by condenser 16a so that the anode recovery after firing forces the grid back to its stabilized voltage point thereby preventing ill-effects due to the long time constant on the grid. The capacitor 16a allows the potential of trigger elect-rode 5 to restore much faster than does capacitor 16, due to the high resistance 14. Furthermore, a rectifier 20 may be included in series with the input circuit in a sense to prevent positive pulses being fed back into the input circuit and a resistance 21 is provided to bleed a small cur rent through the rectifier in the absence of input pulses at terminal 17. The bleeding current for rectifier 20 serves to hold auxiliary cathode 6 at a slightly positive potential. A negative pulse applied at terminal 17 cuts oil this current through the rectifier 2t), and the auxiliary cathode potential drops slightly to initiate the discharge in the tube.

As mentioned above, circuits according to the invention possess the distinctive feature of better charge sensitivity than has hitherto been achieved with cold cathode tubes. Other features possessed by the circuits of the present invention include a low capacity leading on the pulse source, a sensitivity substantially independent of anode voltage over a reasonable range and high stability. This last feature is attributable to the fact that should the condenser 16 or 16a begin to discharge into the tube it does so to the auxiliary cathode 6 which has very little capacity on it and hence there is little chance of a glow discharge being set up which would cause oscillation.

The high quenching current characteristic inherent of the auxiliary cathode type of tube is preserved.

It is to be understood that the invention is not limited to the details disclosed but includes all such variations 3 and modifications as fall within the spirit of the invention and the scope of the appended claims.

What We claim is:

1. A negative pulse trigger circuit comprising a cold cathode electron discharge tube having an anode, a trigger electrode, a main cathode and an auxiliary cathode disposed between said trigger electrode and main cathode, means for setting up a corona discharge between the trigger electrode and auxiliary cathode, circuit means for applying an operating potential between said anode and main cathode, and an input circuit connected with the auxiliary cathode for feeding negative pulses to the tube to withdraw charge and hence increase ionization to set up a glow discharge between the trigger electrode and the main cathode so that the tube discharges between said anode and main cathode, said circuit means including means for quenching the glow discharge in the tube.

2. A negative pulse trigger circuit as claimed in claim 1, further including a rectifier connected in series with the input circuit in a sense to prevent positive pulses from being fed back to the input circuit and a connection to feed a small current through the rectifier for maintaining said auxiliary cathode at a slightly positive potential in the absence of input pulses.

3. A cold cathode electron discharge tube circuit adopted for triggering with negative input pulses comprising a cold cathode electron discharge tube having at least an anode, a trigger electrode, a main cathode and an auxiliary cathode between trigger electrode and main cathode, a connection between a source of positive potential and said anode comprising a quench resistor, a connection from said source of positive potential including a resistor and the trigger electrode/auxiliary cathod gap whereby corona discharge can be set up between the trigger electrode and auxiliary cathode gap, an input circuit connected with the auxiliary cathode for withdrawing charge on receipt of a negative pulse at the input circuit so that the voltage drop across said gap increases to set up glow discharge between trigger electrode and main cathode, a condenser connected with the trigger electrode to be disehargeable between the trigger electrode and main cathode and a condenser connected to he discharge able between anode and main cathode.

4. A cold cathode electron discharge tube circuit as claimed in claim 3, wherein the condenser connected with the trigger electrode is connected between said trigger electrode and said anode.

5. A negative pulse trigger circuit, as claimed in claim 2, wherein said connection includes a resistor.

References Cited in the file of this patent UNITED STATES PATENTS 1,262,490 Hewitt Apr. 9, 1918 1,680,367 Demarst Aug. 14, 1928 1,863,702 Smith June 21, 1932 1,984,877 Jobst et al. Dec. 18, 1934 

